Despite the violence, anti-Mubarak protesters are still convinced they will prevail.

This morning, after a night of violent clashes that left five dead and 800 injured, anti-regime protesters in Cairo's central square braced themselves for further confrontations with Mubarak supporters.

The battle began Wednesday afternoon and lasted into the early hours of this morning, when the anti-Mubarak protesters regained their ground. Tonight, as clashes continue, they'll fight to hold on. And by the look of things, the square is ready for battle.

Inside Tahrir Square, on the grassy knoll where they have pitched tents to spend long, cold nights, the mood was both triumphant and sad.

"If these demonstrators really are pro-Mubarak—I want to give them the benefit of the doubt—it's a shame," Nazly Hussein tells me. (It's widely believed that many of the pro-Mubarak participants in the rallies were paid thugs.) "Knives, horses, camels, it's so Middle Ages," she exclaims, referring to the men brandishing whips who stampeded anti-regime protesters Wednesday.

Sitting on the ground in front of a tent, the special-education teacher regrets the clashes, but she is sure the protesters will prevail. The night was long, and though today promises more violence, she is determined. "We have exceeded their expectations every time, and we'll continue to do so."

Walking to the scene of yesterday's fierce battles in front of the Egyptian Museum, you have to cross four makeshift lines of defense. At each post, demonstrators calling for Hosni Mubarak's immediate resignation have set up improvised lines.

At the very front, a barricade of metal sheeting forms a makeshift wall. And at noon today, when I stood on a milk crate to peer over the front lines, I could see that men on the other side of the tanks separating the groups were already hurling stones toward another anti-Mubarak stronghold. Of course, this was nothing compared with the Molotov-cocktail assault I watched from my balcony the night before.

Mohammad Ghad, a 30-year-old auditor, stands by the metal sheeting. If there is an assault, he will be the first one hit. He is already wounded, sporting a giant bandage on his head from where a rock hit him yesterday. "I'm not afraid. Millions of Egyptians are not afraid. I have a good job. I'm here for other people, the ones who aren't as lucky as me. If they kill me, I asked my brother to take my place," he told me.

I leave the front line and come across the second point of resistance—trashed cars arranged in a line. Behind that is a metal railing with gaps people can climb through. Suddenly, as I stand in front of the gate, the battle cry sounds. Men bang sticks against metal in unison; the ominous sound summons guys from other parts of the square. They pour in calmly, as if marching to war. It's a patient kind of battle, in which you walk toward your opponent. Between the lines, hunched people gather broken bits of the sidewalk in sacks. The rubble will later serve as ammo for the people at the front.

Nevine Immam, a mother of three, is one of the people gathering rocks. "All the past demonstrations had been peaceful. We had no weapons. Then they started with guns, horses, and camels. The last thing we had to defend ourselves with were stones," she says. Nevine is eager to throw some herself, but she thinks there won't be room for her to aim. "I will pass the rocks on, but if I find space to throw a rock, I will," she vows and smiles.

The last line of defense is human. Men link arms to form a human wall across the broad boulevard. People passing into the square are asked for ID and patted down. "We found weapons inside the square," the young woman who frisked me said. "We don't know where they are coming from."

Behind the line of men is a makeshift clinic. As I walk by, a man who was a Muslim Brotherhood candidate in Egypt's parliamentary elections walks by with his followers. After him, a line of professors from Al Azhar University, the Islamic world's most prominent institution of learning, walk forward, linking arms.

Back inside the square, all is calm as protesters continue to flock to the square. The loudspeaker that is used to keep up morale also announces the names of the missing. Volunteers continue to bring in water, juice, and food, but there seems to be less available today, and it's hot, so people are thirsty. Later I hear that plainclothes police prevented many from bringing in supplies.

"It's like a utopia here. We're really organized. We have a self-sustaining city. At 6 a.m. there is a fuul cart, [fuul is a popular Egyptian dish], a kiosk selling cigarettes, people are passing out food and water, [there's] a night watch," Nazly tells me.

As we sit on the ground, a man walks by holding a trash bag. He yells the name of Mubarak's ruling party as he calls for rubbish: "National Democratic Party! National Democratic Party!"

As the day drags on, and Mubarak clings to power, the atmosphere is buoyant. But whether the besieged protesters can maintain their city within a city is another story. Once again today, everyone repeats that they'll stay until the bitter end.

As I exit the square, I step over neatly arranged rows of rocks. Men sit on the sidewalk perusing newspapers. It's all calm until the battle cry sounds.

Sarah A. Topol is a journalist based in Cairo. She has reported from Yemen, Libya, the United Arab Emirates, Israel, Gaza, and the West Bank. Her writing has appeared in the Atlantic, Foreign Policy, Newsweek, and the New Republic, among others.